The present invention relates, generally, to liquid crystal display assemblies and, more particularly, relates to miniature liquid crystal display assemblies constructed to reduce residual stresses.
In the recent past, substantial research and development resources have been directed toward small scale Liquid Crystal Display (LCD) and light valve technologies. These high information content, miniature LCD assemblies enable enhanced availability of graphics, data and video information for employment in high resolution projection displays, such as a reflective LCD projectors, SXGA formats (1,280xc3x971,024 pixel resolution) and even HDTV formats (above 1,000 line resolution), or the like.
Reflective LCD projectors, in particular, are highly desirable since they offer the brightness of traditional three-lamp front-projection systems in combination with the high resolution of an LCD panel. At the heart of these optical engines is reflective liquid crystal on crystalline silicon light valve technology which, when combined with sophisticated optical architecture and the appropriate electronic interface, enables very high resolution, high brightness, large screen displays.
Briefly, as shown in FIGS. 1 and 2, these light valves or small scale LCD assemblies 20 include a die 21 having a pixel array 22 which is generally composed of rows and columns of electrically conductive pathways each forming an individual pixel (not shown). Each pixel can be individually changed to an xe2x80x9conxe2x80x9d condition by selecting the appropriate row and column of pixel array 22. Positioned around or concentrated on one end of the pixel array are a plurality of die bond pads 23 which are internally connected to the pixel array 22 to enable operational control thereof. Selection of the appropriate pixel is controlled by control circuitry, either included within the die 21 or external to the die 21. In either configuration, external control signals may be used to control the functions of the die 21.
A transparent glass plate 24 is typically placed over the die 21 and the pixel array 22, such that a portion of the glass plate 24 overhangs the die 21. The glass plate 24 is usually affixed to die 21 through an adhesive seal 25 which together cooperate to define a sealed volume encompassing the pixel array 22. This sealed volume is then commonly filled with a solution 26 of Twisted Nematic Liquid Crystals (TNLC). The LCD package is completed by rigidly or semi-rigidly mounting the die 21 to a substrate material 27 (e.g., ceramic, metal, plastic, silicon, polyamide, or other substrate materials) for mounting support and heat conductive dissipation for the die.
One problem associated with these LCD panels assemblies is bowing or warpage of individual panels caused by residual stresses acting upon the components during operation. This is particularly noticeable in reflective-type LCD panels which have increased flatness requirements due to the nature of the reflective surface of the die. For example, thermal expansion characteristics, as well as lattice mismatching, can generate significant stresses in the underlying substrate material, therein causing significant bowing of the mirrored surface. The bowing, which translates to a non-planarity of the surface, causes both (1) a non-uniform thickness of the liquid crystal layer between the bowed reflective surface and the planar transmissive top layer, and (2) variations in the path length of the reflected light from different parts of the element, and of the array. These effects compromise the electro-optic properties of the elements and/or array.
Some of these problems have been recently addressed by minimizing or isolating the coupling between the die 21, the transparent plate 24 and the underlying substrate material 27. In effect, the panels are sufficiently isolated from one another so that the transfer of residual stresses therebetween are minimized. Typical of these application may be found in our U.S. patent application Ser. Nos.: 09/130,631, filed Aug. 6, 1998; 09/256,702, filed Feb. 24, 1999; and 09/281,758, filed Mar. 30, 1999, each herein incorporated by reference in their entirety.
Another problem associated with these small scale LCD or light valve assemblies 20 is the formation of an electrical connection with an electrical interface (not shown) for operation thereof. Typically, direct electrical connections to the die bond pads 23 of the die 21 are unacceptable since a significant amount of mechanical stress would be imparted upon its display unit by the electrical connector of the electronic interface. To address this situation, the electrical interconnection is performed through a flex circuit 29 mounted to the substrate, and which functions as an isolatory buffer. As viewed in FIGS. 1 and 2, the flex circuit 29 includes a plurality of flex circuit bond pads 30 which are typically wire bonded to the die bond pads 23 through bonding wires 31. More recently, a distal ringed coupling portion 32 of flex circuit 29 is adhesively or fixedly mounted to the top surface of substrate 27 for support thereof. Finally, a glob coating 33 is applied to die 21, substrate 27 and the distal end of flex circuit 29. The glob coating 33 (FIG. 2) further normally encapsulates the bonding wires 31 and the die and flex circuit bond pads 23 and 30 without obscuring a view of the pixel array 22 through the glass plate 24.
While this approach is advantageous in several respects, namely, providing a relatively stress-free electrical connection between the die 21 and the electrical interface, the flex circuit 29 poses numerous manufacturing challenges. For instance, the flex circuit 29 is often mounted to the substrate 27 in the early stage of the component assembly. Although one end of the flex circuit is secured to the LCD package, the other end is free to move and is often in excess of five inches. Handling of this combination, thus, becomes substantially more cumbersome and difficult to control during subsequent manufacture. Specially designed palates and assembly fixtures have been developed, which are longer than standard automated fixtures, to secure the package and flex circuit tail for automated manufacture. Accordingly, the tooling costs are increased due to their specific use, while at the same time requiring a larger amount of manufacture space.
Moreover, the flex circuit 29 itself is relatively costly to implement, and difficult to handle. During manufacture, several additional assembly steps are required to adhere the flex circuit 29 to the substrate 27.
Accordingly, there is a need to electrically connect an small scale LCD assembly to an electrical interface which minimizes residual stress induced upon the cell, as well as reduce the complexity and costs of assembly.
The present invention provides a liquid crystal display package including a liquid crystal cell having a die with a pixel array, and a transparent plate attached to the die. A liquid crystal material is disposed in a gap region between the die and the transparent plate. The display assembly further includes a containment structure adapted to couple to and at least partially receive liquid crystal cell therein, and an electrical connector portion integrated with the containment structure. A plurality of conductive contacts are positioned in the containment structure for secured support thereof, and in substantially stress-free electrical connection with the pixel array. The conductive contacts further are configured to releasably couple to mating conductive contacts of an opposed electrical connector.
In one embodiment, the die includes a plurality of die bond pads in electrical communication with the pixel array, and the substrate includes a plurality of substrate bond pads in electrical communication with the conductive contacts. The substrate includes a plurality of integrally formed circuits electrically coupling respective substrate bond pads to respective conductive contacts. Each conductive contacts includes a pin portion extending outwardly from the containment structure which is formed for mating cooperation with a respective mating conductive contact of the opposed electrical connector.
In another aspect, the containment structure includes a substrate defining a cavity which is formed and dimensioned for at least partial receipt of the liquid crystal cell therein. A support material is included between the liquid crystal cell and the containment structure to support the liquid crystal cell in a floating manner within the containment structure.
In yet another embodiment, the display assembly includes a plurality of spaced apart stabilizers arranged to couple edge portions of the liquid crystal cell to the containment structure without adhering a bottom surface of the liquid crystal cell to a bottom surface of the containment structure. These stabilizers are sufficiently compliant such substantial stresses are not induced in the LCD assembly.
In another aspect of the present invention, a support substrate device is provided for use with a liquid crystal cell which includes a die and a transparent plate attached to the die. The dies includes a pixel array, and a plurality of die bond pads in electrical communication with the pixel array. The substrate device includes a substrate member defining a cavity formed and dimensioned for at least partial receipt of the liquid crystal cell therein. A plurality of substrate bond pads are positioned along a surface of the substrate member. The substrate bond pads are electrically coupled to respective die bond pads of the liquid crystal cell. The support substrate device of the present invention further includes a plurality of conductive contacts each positioned in the substrate member for secured support thereof. Moreover, each conductive contact is configured to releasably couple to mating conductive contacts of an opposed electrical connector. A plurality of circuit members are disposed in the substrate member in a manner electrically connecting respective substrate bond pads to respective conductive contacts.